Automatic mold cleaning

ABSTRACT

Graphite molds are provided with a refractory coating which must be removed and renewed between each pour. An apparatus and method are provided for sand blasting the coated mold surfaces under controlled conditions to remove the refractory coating without eroding the graphite mold.

Elnited States Patent [191 Germain et a1.

' Dec. 17, 1974 AUTOMATIC MOLD CLEANING Inventors: Andrew Gerald Germain, Itasca;

William George Dressel, Elk Grove Village, both of 111.; Louis Sandor,

Hammond, 1nd.

Assignee: AMSTED Industries Incorporated,

Chicago, 111.

Filed: June 4, 1973 Appl. No.: 367,355

US. Cl. 51/319 Int. Cl. B24c 1/00 Field of Search 51/319, 320, 321, 8, 14,

[56] References Cited UNITED STATES PATENTS 2,479,299 8/1949 Biggs 51/ 2,951,319 9/1960 Kornhaus... 51/8 3,103,765 9/1963 Nolan 51/8 Primary ExaminerDonald G. Kelly [57] ABSTRACT Graphite molds are provided with a refractory coating which must be removed and renewed between each pour. An apparatus and method are provided for sand blasting the coated mold surfaces under controlled conditions to remove the refractory coating without eroding the graphite mold.

7 Claims, 6 Drawing Figures PATENTEB 5531 3.854, 899

sum 3 9 43 PATENTEL w new SHEET UF 4 1 AUTOMATIC MOLD CLEANING Cast steel articles, including railway car wheels, may be advantageously poured in permanent graphite molds. Both to protect the casting surface of such molds from excessive erosion and to eliminate defects on the surface of articles cast in such molds, the mold surfaces are spray coated with a refractory coating of quartz, zircon, crystobalite or the like. After each, use of the mold, the coating must be removed and a new coating applied before the mold can be reused. In prior practice, the coating was removed by manually rubbing the coated surface with, for example, steel wool or burlap. This method of removal was not only time consuming and expensive but due to the mold temperature being at approximately 550 F., the cleaning was incon-' sistent and defects occurred in the cast articles in areas corresponding to improperly cleaned mold areas. A further disadvantage was that the rubbing action wore off the sharp corners at the mold parting line, resulting in fins on castings. poured in such molds. Such worn conditions could only be corrected by the costly and time consuming job of re-machining the mold surface. The high temperature of the molds also contributed to a high turnover of the operators assigned to the cleaning job, and the proximity of the'operators to the finerefractory particles constituted a .potential healthhazzard.

It is a primary object of the present invention to pro- I surface by controlled blasting of the surface with properly selected abrasive particles and a blasting force suf ficient to remove the coating but insufficient to erode the material'of which the mold is made.

These and other objects will become apparent from the following description and accompanying drawings wherein:

FIG. 1 is a front elevation view of the preferred embodiment of the moldcleaning device;

FIG. 2 is a view similar to FIG. 1 but with certain portions shown in greater detail while eliminating other portions;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a sectional view taken along the line 44 of FIG. 2;

FIG. 5 is a vertical sectional view taken through the sand spray gun; and

FIG. 6 is an enlarged sectional view of the nozzle portion of the sand gun.

Referring to the drawings and particularly to FIGS.

1 and 2, the device comprises a framework 10 including a plurality of vertical members 12 and cross members 14. The frame straddles a conveyor, shown in phantom at 16, arranged to carry a succession of molds 17 into position for cleaning. Supported on themes members 14 is a reservoir 18 for supplying the sand to the spray cleaning device. The sand is fed fromthe reservoir through a feed pipe 20 and the flow thereof may be controlled'by a shut-off valve 22, 'whichmay be, for

example, a conventional solenoid operated slide valve.

The basic support for the sand cleaning portion of the arrangement comprises .a rotatable drive assembly,- generally indicated at 23, which includes a bottom ring 24 having mounted thereon a plurality of spacer blocks 26 to which is secured a horizontally disposed drive sprocket 28. Mounted in each spacer block 26 is an angularly disposed upper roller bearing 30 and a lower roller bearing 32 which ride an opposed-bearing surfaces 34 and 36 of a stationary bearing ring 38 secured to frame members 12. Secured to sprocket 28 for rotation therewith are a pair of opposed parallel drive plates 40, the purpose of which'will be explained hereinafter. 5

At a point between the drive assembly 23 and the cross members 14 there are provided a pair of spaced trunnion bars 42 having opposed depending lugs 44 (see also FIG. 4) from which project inwardly thereof trunnions 46. Suspended for pivotal motion on the trunnions'46 is a universal joint 48 (FIGS. 2 and 4) having bearings 50 receiving the trunnions. The joint 48 also is provided with a pair of bearings 52, at right angles to the bearings 50, arranged to receive opposed block is provided with an opening communicatingwith a funnel 66 secured to the block and positioned below the reservoir 18. An air inlet 68 is provided whereby air can be forced through the gun into the space between the inner and outer pipes.

The nozzle portion of the spray gun is indicated generally at 70 and is shown in greater detail in FIG. 6'. Referring to this figure, it is seen that the outer pipe 62 is counterbored to receive a nozzle adapter 71. The upper inner portion of the nozzle adapter is tapered upwardly and outwardly sotha't air may flow through an air passage 72 between the two concentric pipes of the gun and along the tapered surface 74 through a constricted air outlet- 76. The blast of air through the constricted outlet 76 produces a slight negative pressure, or vacuum, at the sand orifice, which may be varied by regulating the air pressure so as to modulate the velocity of the exiting sand. The separate adapter is provided primarily to accommodate variable blasting requirements. The lower end of the inner pipe 60 is open as at 78 to provide an outlet for the sand.

It is seen from the above that the sand gun assembly, being mounted in a universal joint, is free to pivot in any direction but is not free to rotate about its longitu- Also secured to the bearing block for rotation therewith is a gear box 90 having an input shaft 92 on which is mounted a sprocket 94 connected by a chain 98 to a sprocket 96 non-rotatably secured to the outer pipe 62 of the sand gun. The output shaft 100 of the gear box has mounted thereon a cam bar, or crank, 102 carrying at each end thereof cam wheels 104 and 105 The cam wheels are offset as best seen in FIG. 2 so that, at any particular time, only one of them is free to contact a cam plate 106 which is carried by a plurality of cam plate supports 108 welded or otherwise secured to drive plates 40. In the present device and to accommodate the usual range of sizes of wheel molds, the cam plate 106 has been positioned at an angle of approximately from the vertical. However, this angle may be varied considerably without changing the basic principle of operation of the device.

Also secured to the sprocket 28 for rotation therewith isa vane 116 movable through the sensing portion of an electric pulse counter 118.

In order to operate the sand blasting apparatus in a mold cleaning operation, the cope or drag portion of a mold from which a casting has just been removed is positioned beneath the sand gun as shown in FIG. 1. The shut-off valve 22 is opened to feed sand into the funnel 66 and thence through the inner pipe 60, while air is admitted through inlet 68 into the air flow passage 72. Simultaneously the sprocket 28 is rotated by means of a suitable motor, preferably at a speed of about fifteen revolutions per minute, thereby rotating the entire drive assembly 23 including the base plate 24 and the opposed drive plates 40. The drive plates 40 are parallel and positioned at a distance which is slightly greater than the outside diameter of the guide wheels 88 and, as they rotate, they will, through the guide wheels, rotate the bearing block and the components affixed thereto. Because of the fact that the sprocket 96 is nonrotatably secured to the'sand gun, the sprocket 94 is forced to move in a circular path about the longitudinal axis of the sand gun. causing the input shaft 92 of gear box 90 to rotate at the same R.P.M. asthe sprocket 28. With a preferred 20 to 1 reduction in the gear box, the output shaft 100 will rotate at l/20 of the speed of the sprocket 28. This rotation, in a counter-clockwise direction, rotates the crank 102 so as to urge the cam wheel 105 against cam plate 106. The Gem wheel of necessity rolls up the plate thereby pivoting the sand gun outwardly toward the position shown by the phantom lines in FIG. 2. A slot 120 is provided in sprocket 28 to accommodate the movement. The pivotal motion of the sand gun, together with the rotational motion of the bearing block and its components, causes the nozzle end of thesand gun to move in a spiral path outwardly across the mold surface which is to be cleaned.

The device is timed so that one outward and inward cycle of the gun is completed in ten revolutions of the sprocket 28 and one half of a-revolution of the output the sand gun per each unit of time is approximately constant. It is possible therefore to provide complete cleaning of all areas of the mold with a minimum of blasting and consequently with a minimum of erosion of the mold surface. a

Through a complete cycle, the sand gun, which was originally positioned at the center of the mold, was moved radially and circularly in the spiral path out to the mold periphery and then on a similar spiral path back to the center line of the mold to complete the cycle. Meanwhile the vane 116 with each revolution of the gear 28 was passing the electronic counter 118,.

which may be regulated in a conventional manner to shut off the flow of sand after a predetermined number of revolutions of the sprocket 28 and to stop the device completely after another predetermined number of revolutions (preferably 10) which is a complete cleaning cycle.

Because the apparatus was designed to treat softv material such as graphite, it has been found most'advantageous to utilize roundsilica sand of about 135 to 150 A.F.S. fineness. If the sand is appreciably courser, mold erosion could occur while if the sand is appreciably finer, the efficiency of the cleaning will be decreased.

' original position being about 24 inches from the mold surface and utilizing air pressure at about pounds per square inch. As the gun swings outwardly toward shaft 100. Furthermore, because'the cam wheel 104 is movingin approximately a circular path, the speed at which the pivoting action of the sand gun takes place is variable, and the rate of variation'is in the form of a modified sinusoidal curve whereby the laterally outthe periphery of the mold, the nozzle is moving in an arcuate radial path and therefore-is moving away from the mold surface. To obtain a constant cleaning effectiveness, it has been found that air pressure is preferably gradually increased from the starting. pressure of about 40 PSI toapproximately 50 PSI .at the outer limit of the cycle. Obviously these distances and pressures may be varied and adjusted as required at the time of the original set up of the equipment. However, to accommodate the above variables, it is preferred to use a conventional variable air pressure regulator programmed such that the pressure will automatically increase from 40 pounds per square inch at minimum gun angle to approximately 50 pounds per square inch in the maximum gun angle. This of course is accomplished with conventional equipment which does not form part of the present invention.

The apparatus is also provided-with an exhaust system whereby the used sand and the coating removed 4 thereby are sucked away from the mold and into a separator wherein the sand, which is reusable, is separated from the coating dust which is discarded.

What is claimed is:

1.-A method of removing a foreign material from the spaced from themold; then dropping sand through an inner gun passage and forcing air through an outer gun passage so that sand is forcefully ejected against the mold surface, while simultaneously moving the lower end of the gun in a spiral path toward the periphery of the mold, the rate of speed of the circular component of said path being constant and the rate of speed of the radial component of said path being at a decreasing rate. a

2. A method according to claim 1 and including the step of increasing the air pressure and thereby the sand velocity as the lower end of the gun moves from the axis to the outer periphery of the mold.

3. A method according to claim 1, wherein the sand is silica and of about 135 to 150 A.F.S. fineness.

4. A method of removing a mold coating from the casting surface of a graphite mold, comprising the steps of:

suspending a sand spray gun on the axis of the moldsand through the spray gun and against the mold,

surface, moving the spraygun in a spiral path toward the periphery of the mold, the rate of outward radial motion of the gun decreasing substantially proportionally to the increase in distance from the mold axis so that approximately equal areas of the mold are cleaned in equal increments of time.

5. Sand blasting apparatus comprising, a frame; a sand blasting gun having its upper end suspended from the frame for universal pivotal movement; a first means for moving the lower end of said gun in a radial direction; and a second means for simultaneously moving the lower end of said gun in a rotary path so that the combined motions cause the lower end of the gun to move in a spiral path, said first means comprising a rotatable shaft movable with said gun in radial direction; a crank secured to the shaft for rotation therewith; -a cam wheel at the outer end of the crank; a cam plate immovable in a direction radially of said gun; said cam wheel being movable, upon rotation of said shaft, along the cam plate to force said shaft and said gun radially outward at a decreasing rate of speed.

6. Sand blasting apparatus according to claim 5 wherein said first means includes a bearing block rotatably mounted on the gun below the pivotal axis thereof; a gear box secured to said block for rotation therewith; a sprocket secured to the gear box input shaft; a sprocket nonrotatably secured to the gun; a chain interconnecting said sprockets; an output shaft on the gear box; a cam bar secured to the output shaft forrotation therewith; a cam wheel carried by the cam bar; and an angularly disposed cam plate engageable by the cam wheel as the output shaft rotates. v

7. Sand blasting apparatus according to claim 5 wherein said second means comprising a pair of guide wheels rotatably mounted on opposite sides of said block for rotation therewith, the axis of each wheel being disposed to pass through the pivotal axis of the gun; a rotatable driveassembly carried by the frame and positioned concentric with the gun and below said bearing block; spaced parallel guide plates secured to the upper portion of said drive assembly for rotation therewith; said guide plates straddling said guide wheels and being engageable therewith; and means for rotating said drive assembly. 

1. A method of removing a foreign material from the surface of a graphite mold, comprising the steps of: suspending a sand spray gun from a universal joint over the axis of the mold with the lower end of the gun spaced from the mold; then dropping sand through an inner gun passage and forcing air through an outer gun passage so that sand is forcefully ejected against the mold surface, while simultaneously moving the lower end of the gun in a spiral path toward the periphery of the mold, the rate of speed of the circular component of said path being constant and the rate of speed of the radial component of said path being at a decreasing rate.
 2. A method according to claim 1, and including the step of increasing the air pressure and thereby the sand velocity as the lower end of the gun moves from the axis to the outer periphery of the mold.
 3. A method according to claim 1, wherein the sand is silica and of about 135 to 150 A.F.S. fineness.
 4. A method of removing a mold coating from the casting surface of a graphite mold, comprising the steps of: suspending a sand spray gun on the axis of the mold and spaced from the mold, and then, while forcing sand through the spray gun and against the mold surface, moving the spray gun in a spiral path toward the periphery of the mold, the rate of outward radial motion of the gun decreasing substantially proportionally to the increase in distance from the mold axis so that approximately equal areas of the mold are cleaned in equal increments of time.
 5. Sand blasting apparatus comprising, a frame; a sand blasting gun having its upper end suspended from the frame for universal pivotal movement; a first means for moving the lower end of said gun in a radial direction; and a second means for simultaneously moving the lower end of said gun in a rotary path so that the combined motions cause the lower end of the gun to move in a spiral path, said first means comprising a rotatable shaft movable with said gun in radial direction; a crank secured to the shaft for rotation therewith; a cam wheel at the outer end of the crank; a cam plate immovable in a direction radially of said gun; said cam wheel being movable, upon rotation of said shaft, along the cam plate to force said shaft and said gun radially outward at a decreasing rate of speed.
 6. Sand blasting apparatus according to claim 5 wherein said first means includes a bearing block rotatably mounted on the gun below the pivotal axis thereof; a gear box secured to said block for rotation therewith; a sprocket secured to the gear box input shaft; a sprocket nonrotatably secured to the gun; a chain interconnecting said sprockets; an output shaft on the gear box; a cam bar secured to the output shaft for rotation therewith; a cam wheel carried by the cam bar; and an angularly disposed cam plate engageable by the cam wheel as the output shaft rotates.
 7. Sand blasting apparatus according to claim 5 wherein said second means comprising a pair of guide wheels rotatably mounted on opposite sides of said block for rotation therewith, the axis of each wheel being disposed to pass through the pivotal axis of the gun; a rotatable drive assembly carried by the frame and positioned concentric with the gun and below said bearing block; spaced parallel guide plates secured to the upper portion of said drive assembly for rotation therewith; said guide plates straddling said guide wheels and being engageable therewith; and means for rotating said drive assembly. 